Steam bending mahogany

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Angelo
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Steam bending mahogany

Postby Angelo » Fri Feb 03, 2017 3:31 pm

So I am attempting to steam bend 3/4 mahogany for the carlings on my malahini build. They are roughly 9'6" and ripped to 5 3/4". My box gets up to 200 degrees, I placed a meat thermometer at the exit end to make sure. They bend right around my jig but invariably they end up cracking. I am using 3/4 x 4 deck boards as testers because I am loathe to crack the wider stock. I have tried soaking them in a solution of fabric softener and water for several days. Typically they're in the box at 200 for an hour. I have no idea what the problem could be. Any suggestions?

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Dave Grason
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Re: Steam bending mahogany

Postby Dave Grason » Fri Feb 03, 2017 4:00 pm

How long are you leaving the boards in your steam box?

Approximately one hour per one inch of thickness I believe is about right. This is an edit. I somehow skipped past that the first time I read it where you said about an hour.

Also, as far as tempurature goes, if there's steam going into the box and, of course, leaking out here and there, you should be good to go. It's simple elementary school physics. The water boils at 212 degrees and turns to steam but then it's going to be condensing and turning back into as it goes into your steam box. So the 200 degrees you're claiming sounds correct to me.
Last edited by Dave Grason on Fri Feb 03, 2017 4:28 pm, edited 1 time in total.
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Angelo
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Re: Steam bending mahogany

Postby Angelo » Fri Feb 03, 2017 4:04 pm

Here's some pics
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Angelo
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Re: Steam bending mahogany

Postby Angelo » Fri Feb 03, 2017 4:06 pm

When the boards first go in temp immediately drops to like 180. I assume it's the cooler wood absorbing the heat takes about five minutes or so to get back to 200 then I start the clock at an hour.

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Dave Grason
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Re: Steam bending mahogany

Postby Dave Grason » Fri Feb 03, 2017 4:30 pm

Ok, remember...

steamed wood cells cannot stretch even when they are super heated like that. They can ONLY compress.
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Angelo
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Re: Steam bending mahogany

Postby Angelo » Fri Feb 03, 2017 4:43 pm

I understand that they won't stretch what I need is a solution to making this bend.

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hoodman
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Re: Steam bending mahogany

Postby hoodman » Fri Feb 03, 2017 4:46 pm

I'm not sure I understand. You're steaming deck boards and they are cracking? What kind of wood is that? Or are you steaming the mahogany and it's cracking?

Angelo
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Re: Steam bending mahogany

Postby Angelo » Fri Feb 03, 2017 4:54 pm

It's mahogany decking leftover from a farmers porch I built over the summer. Soaked for three days and then in the steamer at 200 degrees for an hour.

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jenko
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Re: Steam bending mahogany

Postby jenko » Fri Feb 03, 2017 5:44 pm

that wood looks more like merbau which is very brittle hard and water resistant

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Roberta
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Re: Steam bending mahogany

Postby Roberta » Fri Feb 03, 2017 5:49 pm

I stem using 6 mil plastic sheeting rolled into a tube and a wall paper steamer for my steam source. I can put the wood in the plastic sleeve and stick the steamer into one end, letting the steam flow out the other end. The wood is clamped about where it will go and then the steaming process is started. I will slowly bend the wood in place while still steaming until I get it clamped into the final position. The rolled plastic sleeves will allow me to continue steaming all the way to position. I tried steam boxes before and I think on smaller wood, the wood cools to fast.

Roberta
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PeterG
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Re: Steam bending mahogany

Postby PeterG » Fri Feb 03, 2017 6:20 pm

There's a chance that wood was kiln dried, which makes steam bending much more difficult if not impossible.

I noticed you are making the carlings 3/4" thick, even though the Malahini plans call for 1/2" thick ones. Thinner stock would be more easily bent to shape, steaming them may be more successful. If you really do want 3/4 " thick carlings you could laminate them, from two 3/8" thick layers or three 1/4" layers. More work yes, but easier shaping, no splitting and a bit stronger.
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Angelo
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Re: Steam bending mahogany

Postby Angelo » Fri Feb 03, 2017 6:51 pm

It was most definitely kiln dried. That's why I was soaking it but some reading I have been doing says the lignin had all ready been set in the kiln. Thought about pushing through the thickness planer and milling it down to half inch. I saw an online video where someone used a poly sleeve and bent a pretty rugged piece, 2x4,of mahogany but it was green lumber. Contemplated the poly but my only concern is it's winter in New England and I can only heat my workspace up to 45 or 50 on a good day. Will poly be able to hold heat long enough?

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Roberta
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Re: Steam bending mahogany

Postby Roberta » Sat Feb 04, 2017 7:27 am

Using the poli sleeves will allow you to bend while continuing to steam the wood. That way it never warms up until you shut off the steam when the bend is completed. You can use ratchet straps to slowly pull the bend into place and then clamp the wood in place while it cools. Can't say if the kiln drying prohibits steam bending, but slow bending while the steam is running through the sleeves has to be better than pulling the wood out of the steam box and watching it rapidly cool while you try to bend it before it cools.

Roberta
Roberta "Queen of the Boat Builders"
Built Zip "Oliver IV", Super Spartan "Jimmy 70", and Torpedo "The Glen L".

Angelo
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Re: Steam bending mahogany

Postby Angelo » Sat Feb 04, 2017 9:48 am

That's what I just heard down at the cape cod boatbuilders show. I was also told that setting the piece with compression straps, drawing is crude but anyways it goes like this. By setting end blocks and comnecting the two with steel straps, as simple as the stuff they bundle lumber with at cheapo depot, the tension side of the bend will not be allowed to elongate essentially putting the entire piece in a state of compression. I think this is what Dave was getting at
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Angelo
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Re: Steam bending mahogany

Postby Angelo » Sun Feb 12, 2017 9:13 am

1x8 KD Mahogany. Three days soaking in a solution of water and fabric softener. One hour in the box at 200 degrees. Out of box compression straps applied, and wrapped in poly. Shout out to the queen. Slow bent and cooked on the jig fifteen minutes. Bent like a champ.
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